In the following, the word “avatar” will be used broadly to designate a computer-generated, usually three-dimensional, representation of a human or animal body, a humanoid or zoomorphic creature, or even a vegetable or an inanimate object (e.g. a piece of furniture such as a sofa). Most often, however, the avatar will be a representation of a human or humanoid body. The avatar may be designed ab initio, or it may be reconstructed by scanning a real body or object.
The words “virtual garment” or “virtual upholstery” will refer to a computer-generated bi-dimensional or (most often) three-dimensional representation of clothing, upholstery or the like, suitable to be worn by an avatar. The virtual garment may be a model of a “real” garment suitable to be manufactured in the physical world. In the following, only the case of garments will be discussed, but all equally applies to upholstery.
Avatars and virtual garments are preferably “three-dimensional” (3D). Hereafter, a “three-dimensional” object will be an object—or a digital model thereof—allowing a three-dimensional representation, which allows the viewing of its parts from all angles.
The word “pattern” will designate a piece of fabric, leather or other flexible material suitable to be used to manufacture a garment. A garment is most often manufactured by assembling several patterns by their edges. Patterns are usually considered two-dimensional, as they are developable (they can lie flat on a plane) and their thickness is negligible (smaller by at least two orders of magnitude) over their other dimensions.
Computer-aided techniques have been widely used in the development process of pattern-making in the fashion industry. Specifically, CAD (Computer Aided Design) and CAM (Computer Aided Manufacturing) systems have helped to produce digital 2D patterns which are then used to manufacture garments. These patterns are generally described as two-dimensional boundary curves enriched with additional information needed to physically construct the final garment. Several CAD systems exist on the market from companies such as Lectra, Gerber Technology, Optitex, Assyst GMbH (Human Solutions Group), Clo3D (Marvelous Designer). The modules they propose present common characteristics and are mainly focused on 2D patterns development, CAD-CAM management and manufacturing (e.g. pattern layout and cut with automatic machine).
With the emergence of 3D, virtual clothing is becoming a standard and it requires new techniques to assemble virtually the 2D patterns in order to get the virtual garment. Unfortunately, the 2D patterns created with standard CAD systems lack information about how to place them efficiently. In fact, most of the existing 2D CAD pattern models are conceived for design or cutting of unassembled textile parts. Thus, they do not provide assembly and positioning instruction in order to place them related to the model body.
FIG. 1 shows the general pipeline of a 3D virtual garment prototyping method. More details are provided in [1].
First of all, a set of 2D patterns P of the virtual garment and an avatar AV are provided. As it has been already mentioned, 2D CAD patterns may come from standard industry pattern-marker software; in some cases, they may be obtained by scanning and digitally processing “physical” patterns made of paper. The 3D avatar is created by an artist, generated from anthropometrical survey analysis or obtained from body measurements (e.g. 3D scanning). Then the patterns are positioned around the avatar and assembled using seam definitions. Finally, physical simulation is performed to drape the assembled garment G.
Pattern positioning and seams definition are crucial since they define the starting state for the garment simulation; if they are not provided or not well defined, the simulation will fail. Manual positioning of the pattern is a tedious and time-consuming (and therefore expensive) task for the garment designer, who has to pick-up 2D patterns, to move them around a 3D space—i.e. with six degrees-of-freedom (three translational and three rotational) and often to change the observation point of the scene. For this reason, research works have been performed concerning the automatic or semi-automatic pre-positioning of patterns and proposed by some commercial software like Vidya from Human Solutions. However, their results are not entirely satisfactory.
The most common approach consists in laying the patterns over developable (e.g. cylindrical or frustoconical) bound surfaces encompassing different parts of the avatar (e.g. its limbs and trunk). See [1] and [4]. It is also known to use “snap points” on the avatar (or on the bound surfaces) in order to allow fast pre-positioning (see [4]). An inconvenience of these approaches is that bound surface and/or snap points have to be defined manually for each avatar. In practice, the garment designer is constrained to use a limited library of avatars for which these elements have been pre-defined. Moreover the positioning is quite approximate (bound surfaces oversimplifies the shape of the avatar), and manual fine-tuning of the pattern position is often required.
Reference [5] uses 2D silhouettes to assist in pattern positioning. This approach is basically two-dimensional and does not allow a 3D fitting of the pattern around the avatar.